1. Field of the Invention
The present invention generally relates to electrical connectors, and more particularly, to connectors designed to compensate for crosstalk induced on a conductor pair from other conductor pairs.
2. Related Art
In conventional electrical communication systems, such as these for telephony and data applications, a balanced signal is transmitted over a communication path composed of a pair of conductors that are not grounded. The balanced, or differential, signal constitutes the voltage difference between the individual conductors in the pair without regard to the absolute voltages present on each conductor. In such conductor pair transmission systems, an electromagnetic field is often created that interferes with signals on adjacent conductors. As the frequency of the transmitted signal increases, the effects of this interference become even greater. This interference is electrical noise and is commonly referred to as crosstalk.
Crosstalk can occur at any place where conductor pairs are in close proximity. A particular type of crosstalk called near-end crosstalk (NEXT) occurs at the near ends of communication or transmission paths, since the near end of a path may have eight or more wires situated close together over a very short distance.
NEXT is the portion of a transmitted signal that is electromagnetically coupled back into the received signal. For example, NEXT occurs in telephone communication whenever a separate communication is overheard on a telephone. In the case of computer networks, NEXT occurs when a strong signal on one pair of wires is picked up by an adjacent pair of wires. Two different types of NEXT can be induced in an adjacent pair of conductors, namely, differential-mode crosstalk and common-mode crosstalk.
Differential-mode crosstalk corresponds to a differential or balanced signal that is induced in the adjacent pair, where the currents in the two wires of that pair flow in opposite directions. Common-mode crosstalk corresponds to a common-mode or an unbalanced signal that is induced in the adjacent pair, where the currents in the two wires of that pair flow in the same direction. When a differential-mode signal exists on one pair, it may induce both differential-mode and common-mode crosstalk on an adjacent wire pair. The actual magnitude for each crosstalk mode is influenced by a number of factors, such as the relative proximities of the individual wires of the pair carrying the signal to the individual wires of the adjacent pair experiencing the crosstalk.
In attempts to reduce or compensate for NEXT crosstalk in communication paths, compensating signals are often introduced to counteract the effects of the crosstalk disturbances or noise. Such crosstalk compensation is achieved by connecting coupling devices, such as capacitors or capacitance-producing patterns on printed wiring boards, between different pairs of conductors of a multi-pair connector. Customarily, multiple compensation stages are needed because, at high frequencies, crosstalk compensating signals cannot be introduced that are exactly 180 degrees out of phase with the offending crosstalk through utilization of a single compensation stage.
For example, U.S. Pat. No. 5,997,358, issued on Dec. 7, 1999, discloses a multi-stage compensation scheme. In accordance with this scheme, crosstalk compensation is introduced either by creating crossovers of certain conductors within the connector, or by appropriately placing capacitors to compensate for differential-mode crosstalk. U.S. Pat. No. 5,967,853, issued on Oct. 19, 1999, describes a multi-stage compensation scheme that uses capacitors between different pairs of conductors to compensate for both common-mode and differential-mode crosstalk. In U.S. Pat. No. 6,270,381, issued on Aug. 7, 2001, a multi-stage compensation scheme is disclosed that uses crossovers between different pairs of conductors to compensate for common-mode and differential-mode crosstalk.
Existing crosstalk compensation schemes used with electrical connectors, such as those described above, are designed to compensate for crosstalk induced in a pair of conductors from an adjacent driven pair of conductors. Such existing crosstalk compensation schemes, however, may actually disturb the crosstalk balance of nearby pairs. A heretofore unaddressed need exists in the industry for a system and method that corrects NEXT crosstalk unbalance introduced by crosstalk compensation schemes.
Accordingly, a need exists to compensate for NEXT unbalance in a pair combination caused by a NEXT compensation scheme deployed on another pair combination. A further need exists for such a compensation technique that could be employed with connectors that are designed to meet the proposed Category 6 cabling standard set forth by the Telecommunication Industry Association (TIA) task group under TIA/EIA-568-B.2-1 (addendum No. 1 to TIA/EIA-568-B.2).